View full sizeWarren Watkins, The Daily Citizen, via The Associated PressCindy and Stephen Bryant examine one of the thousands of dead birds that fell from the sky Saturday near their home in Beebe, Ark.

That supports the theory that fireworks on New Year's Eve spooked the birds and sent them flying into cars, houses and each other and plummeting to their deaths.

The Wildlife Health Center in Madison, Wis., released the results Wednesday.

Arkansas' Game and Fish Commission says the birds didn't test positive for any pesticides. Officials are still awaiting lab results from tests for other toxins and infectious diseases.

In all, up to 5,000 birds rained onto rooftops and into fields in the central Arkansas town of Beebe. One struck a woman walking her dog and another hit a police cruiser.